Sunday picnics have security clearances? The issue is that stripping these security clearances in a purge that appears to be without due process is not what has always been. It is one further piece of evidence of a worrying trend towards an authoritarian approach to politics in America and this is something new.

Furthermore, stripping these security clearances robs the current government of the ability to discuss classified issues with these people. For example, if Marco Rubio wanted to talk to, say, Antony Blinken to access his knowledge regarding foreign policy from the last four years, a lot of that ability will be blocked by Blinken's loss of security clearance.  In other words, the government is losing all the benefit of that experience.

As far as whether or not it is politics.  Of course it is. It is called payback.  

That is the crux of the matter, isn't it? The historical norm for America (derived from a long-held tenet of English common law) has been for due process to be in play: adherence to the established rules of the system which, in the case of the Government enforcing changes on individuals, means the Government's power is restricted by procedural protections. The established precedent is for revocation of security clearances to be subject to review. 

The US Constitution, via the fifth and fourteenth amendments, guarantees an individual the right to conduct business. Any denial change to a security clearance may prevent future employment and is therefore a constitutional liberty interest. If the decision to strip "any active security clearances held by individuals at Perkins Coie" or for, say, Mark Zaid, is purely political payback rather than an issue of national security -- as you state and as seems clear --  then it would seem unconstitutional. In the case of Zaid, who has represented whistleblowers using his clearance for the last thirty years, it restricts his ability to practice law in this way going forward.